In general, an active-matrix liquid crystal display device has a liquid crystal panel, including two substrates with a liquid crystal layer provided therebetween, as a display portion, in which a plurality of data lines as video signal lines and a plurality of gate lines as scanning signal lines are arranged in a matrix on one of the two substrates and a plurality of pixel formation portions are provided and arranged in a matrix at their corresponding intersections of the data lines and the gate lines. The pixel formation portions are components for displaying an image on the liquid crystal panel and each of them includes a TFT (thin-film transistor), which is a switching element having a gate terminal connected to the gate line and a source terminal connected to the data line, and a pixel electrode connected to a drain terminal of the TFT.
Such an active-matrix liquid crystal display device includes a data driver for driving the data lines of the liquid crystal panel, a gate driver for driving the gate lines, a common electrode drive circuit for driving the common electrode, and a display control circuit for controlling the data driver, the gate driver and the common electrode drive circuit.
While in recent years, display devices have advanced to display higher-definition images, the number of signal lines (electrodes) per unit length in display devices, such as active-matrix liquid crystal display devices, which require signal lines (column or row electrodes) in a number corresponding to the resolution of images to be displayed, is increasing significantly as the definition of display image resolution becomes higher. Consequently, when mounting a drive circuit for applying signals to the signal lines, the pitch (hereinafter, the “connection pitch”) between connections of output terminals of the drive circuit to the signal lines on a display panel is extremely fine. In the case of color display devices, such as color liquid crystal display devices, which use three adjacent pixels, R (red), G (green) and B (blue), as a unit of display, such tendency toward a finer connection pitch to achieve higher-definition display images is pronounced especially at the connections of video signal lines to their drive circuit (data driver).
To solve such a problem, until now, there have been proposed some liquid crystal display devices that are configured such that video signal lines are divided into groups of two or more (e.g., three video signal lines corresponding to three adjacent pixels R, G and B), the video signal lines in each group are assigned one output terminal of a video signal line drive circuit, video signals are collectively outputted from all output terminals within one horizontal scanning period during image display (a so-called line-sequential driving system), and the video signals are applied to the video signal lines in each group in a time-division manner.
For example, Japanese Laid-Open Patent Publication No. 2000-29441 discloses a liquid crystal display device in which three analog switches are controlled to sequentially connect three video signal lines, which correspond to three adjacent pixels, R, G and B, to one output terminal of a source driver. Also, Japanese Laid-Open Patent Publication No. 2003-5152 discloses a liquid crystal display device in which two video signal lines are switched so as to be alternatingly connected to one output terminal of a source driver. Furthermore, Japanese Laid-Open Patent Publication No. 2002-244619 discloses an LED display device in which three FETs are controlled to sequentially connect three LEDs, which emit light of their respective colors, R, G and B, to a constant current driver.
In the case of the aforementioned liquid crystal display device with the video signal line time-division driving system, the time of charging each video signal line decreases in accordance with the number of video signal lines in each group, i.e., the number of time divisions by a changeover switch, and when the number of time divisions is m, the charging time for each video signal line is 1/m of that for typical liquid crystal display devices that are not on the video signal line time-division driving system. However, by forming changeover switches with the number of time divisions being m on a liquid crystal panel substrate, it becomes possible to increase m-fold the connection pitch between connections of the output terminals of the video signal line drive circuit to the video signal lines when compared to typical liquid crystal display devices. Also, with such a configuration, it is possible to reduce the number of integrated circuit chips (IC chips) when a video signal line drive circuit consisting of such chips is used for driving a liquid crystal panel. The advantage of such a video signal line time-division driving system is widely known, and the grouping of the video signal lines therefor is often performed such that each group is made up of three video signal lines for transmitting video signals to three adjacent pixels, R (red), G (green) and B (blue).
Also, some display devices, such as the aforementioned active-matrix liquid crystal display devices, which require data or gate lines (column or row electrodes) in a number corresponding to the resolution of images to be displayed, might employ a so-called dot-sequence driving system for sequentially driving the video signal lines, instead of employing the aforementioned line-sequential driving system. The dot-sequence driving system advantageously makes it possible to achieve a simplified device configuration. In the case of the dot-sequence driving system, however, higher-definition display images might result in reduced time of sampling video signals to be provided to the data lines and also reduced time of providing the video signals to the data lines (reduced charging time).
Therefore, in some cases, a so-called phase expansion driving system (phase expansion processing system) is employed to extend the sampling time and the charging time, which, however, results in a more complicated device configuration when compared to the dot-sequence driving system. The phase expansion processing refers to processing for properly displaying an image represented by a high-frequency image signal, in which the duration of an image-representing signal per dot or pixel (hereinafter, referred to as the “per-dot signal duration” or the “per-pixel signal duration”) is extended and the frequency of an image signal to be provided to the liquid crystal panel is reduced. Note that when the phase expansion processing is performed such that the per-dot signal duration is n times the dot clock (pulse repetition) period, the processing is referred to as “n-phase expansion”.
FIG. 8 is a partial configuration diagram of a data driver which is a circuit for driving data lines in a liquid crystal display device in which two-phase expansion is performed. The data driver is supplied with analog video signals AV, which are generated by two-phase expansion being performed for each of the R (red), G (green) and B (blue) colors in a predetermined phase expansion circuit, via six signal lines. A shift register 91 sequentially outputs sampling pulses from flip-flop circuits FF1, FF2, . . . , in an input to output terminal direction. As a result, analog switches in the figure are turned on, so that the analog video signals AV being fed from the phase expansion circuit are supplied to their corresponding video signal lines of a liquid crystal panel, two color pixels at a time, thereby displaying an image (it is assumed here that each color pixel is displayed by three adjacent pixel formation portions for displaying R, G and B colors, respectively).
For example, Japanese Laid-Open Patent Publication No. 5-21036 discloses a configuration of a liquid crystal display device in which four-phase expansion is performed. Also, Japanese Laid-Open Patent Publication No. 1-202793 discloses a configuration of a liquid crystal display device in which signal lines are halved into those connected to pixels in even columns and those connected to pixels in odd columns, and the columns are driven from opposite sides of a panel.